Preorganization of tetrathiamacrocyclic ligands: implications from computed and experimentally determined structures

Abstract

The tetrathiamacrocycles trans-6,13-dihydroxy-1,4,8,11-tetrathiacyclotetradecane (L ¹ ) and its benzo- (L ² ), syn- and anti-dibenzo-substituted derivatives (L ³ and L ^3′ , respectively) have been prepared by conventional methods, and a benzo-substituted-1,4,7,10-tetrathiacyclotridecane (L ⁴ ) was obtained by substitution of o-dichlorobenzene after activation with an organometallic fragment. The structures of L ¹ –L ⁴ and of the four palladium(II) complexes [PdL ¹ ]Cl ₂ ·2H ₂ O, [PdL ² ][PF ₆ ] ₂ , [PdL ^3′ ][PF ₆ ]Cl and [PdL ⁴ ][PF ₆ ] ₂ were determined by X-ray crystallography. All the experimentally determined structures were accurately reproduced by molecular mechanics calculations, using a constant-parametrization scheme. Two parameters for the evaluation of the extent of preorganization of free macrocycle molecules, based on structural and strain-energy differences of the free macrocycles and their corresponding metal complexes, are introduced and discussed on the basis of the experimentally determined and computed structural data for L ¹ –L ⁴ , their metal complexes and other similar ligand and metal complex systems. The implications for the design of new compounds leading to high stability and high metal-ion selectivity are outlined.